Singer's stereo control knob (6)

I believe the answer is:

treble

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'singer's' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for treble that I've seen before include "High-frequency (radio control knob)" , "Score of sixty with one dart?" , "high frequency" , "Chorister; multiply by three" , "Boy chorister" .)

I've seen this clue in The Sun.

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